1. Field of the Invention
The present invention generally relates to the liquid source chemical vapor deposition of metal films as the electrode on capacitors in integrated circuits. More particularly, bis(ethylcyclopentadienyl) ruthenium is used as the liquid source precursor for chemical vapor deposition of ruthenium films at a low temperature in the kinetic-limited temperature regime as the electrode for the application of metal-insulator-metal capacitors.
2. Brief Description of the Related Art
In metal-insulator-metal capacitors, ruthenium is a preferred electrode material for next-generation dynamic random access memories (DRAMs). As the next generation DRAM technology evolves, it will become necessary to use three-dimensional capacitors despite the high-dielectric constant materials employed. The most important characteristics of a capacitor are high dielectric constant and small leakage current even when the electrode film is thin. If the films are being formed for electrodes for DRAM applications, it is advantageous to use a chemical vapor deposition process (CVD).
Chemical vapor deposition is a broad class of processes using controlled chemical reactions to create layers on wafers and is a key process in the development of ultra-large-scale integrated circuit fabrication. Chemical vapor deposition of thin metal films realizes good step coverage and wafer-to-wafer repeatability on complicated topography. However, the source material for CVD processes must be stable and possess good vaporization properties.
The use of liquid source metalorganic precursors for the CVD formation of thin films provides a means of repeatably creating these wafers. CVD precursors for advanced DRAM electrodes and dielectrics have traditionally been solid compounds and although soluble in organic solvents such as tetrahydrofuran, solubility is limited. CVD deposition of films can require high vaporization temperatures and residues are left after vaporization and deposition. Barium strontium titanate thin metal films on a substrate with a BST sputtered film using titanyl bis (dipivaloymethanto) (TIO(DPM)) and titantium tetraisopropoxide (TTIP) organometallic solutions as the CVD liquid source material have been formed.
Traditionally, bis(cyclopentadienyl) ruthenium (Ru(Cp)2) is used to deposit thin ruthenium films on substrates. However, this precursor is a solid at room temperature possessing the concomitant problems of limited solubility in tetrahydrofuran, lower deposition rate and remaining residue after vaporization which could cause particle formation, process drift and prevent precursor transport. Additionally, bis(cyclopentadienyl) ruthenium easily forms a ruthenium oxide film on substrates at low temperatures in the kinetic-limited temperature regime for virtually all process conditions.
It is therefore, advantageous, to use a liquid source for CVD thin film deposition that is a stable liquid at room temperature, yet is less susceptible to oxidation during vaporization and deposition of thin films. Ruthenium films have been deposited on silicon substrates using bis-(ethylcyclopentadienyl) ruthenium. However, these ruthenium films had a large column width and contained large quantities of carbon and hydrogen impurities which resulted in a resistivity greater than that of films deposited using the solid precursor bis-(cyclopentadienyl) ruthenium, although, the resistivity was still sufficiently small to be used as capacitor electrodes.
Bis-(alkyl-cyclopentadienyl) ruthenium complexes, including Ru(EtCp)2, have been synthesized and have been used in a process to produce ruthenium-containing films. These pure ruthenium films were deposited on a silicon substrate at 600xc2x0 C. in a hydrogen atmosphere. Thus, deposition occurred in the mass-transfer limited regime.
The prior art is deficient in the lack of effective means of depositing pure thin ruthenium films on a substrate using a chemical vapor deposition source that is liquid at room temperature and where deposition temperature occurs in the kinetic-limited temperature range. The present invention fulfills this long-standing need and desire in the art.
The present invention provides a method of depositing ruthenium films on a substrate via liquid source chemical vapor deposition wherein the source material is liquid at room temperature and utilizes process conditions such that deposition of the ruthenium films occurs at a temperature in the kinetic-limited temperature regime.
In another embodiment of this invention, there is provided a method of depositing a thin ruthenium film on a substrate by liquid source chemical vapor deposition, using bis-(ethylcyclopentadienyl) ruthenium, by vaporizing the bis-(ethylcyclopentadienyl) ruthenium at a vaporization temperature of about 100-300xc2x0 C. to form a CVD source material gas and forming a thin ruthenium film on a substrate in a reaction chamber using the CVD source material gas and the oxygen source reactant gas such that the substrate has a temperature of about 100-500xc2x0 C. and deposition of the ruthenium film occurs in the kinetically limited temperature regime.
Other and further aspects, features, and advantages of the present invention will be apparent from the following description of the presently preferred embodiments of the invention given for the purpose of disclosure.